实验2
实验任务1
源代码
- t.h
#pragma once
#include<string>
class T {
public:
T(int x = 0, int y = 0);
T(const T &t);
T(T &&t);
~T();
void adjust(int ratio);
static int get_cnt();
friend void output(const T &t);
static const std::string doc;
static const int MAX_CNT;
private:
int m1, m2;
static int current_cnt;
};
- t.cpp
#include "t.h"
#include<iostream>
#include<string>
#include<stdexcept>
const std::string T::doc{"a simple class sample"};
const int T::MAX_CNT = 999;
int T::current_cnt = 0;
T::T(int x, int y): m1{x}, m2{y} {
if (current_cnt == MAX_CNT) {
throw std::runtime_error("T: maximum object count exceeded");
}
++current_cnt;
std::cout << "T constructor called.\n";
}
T::T(const T &t): m1{t.m1}, m2{t.m2} {
if (current_cnt == MAX_CNT) {
throw std::runtime_error("T: maximum object count exceeded");
}
++current_cnt;
std::cout << "T copy constructor called.\n";
}
T::T(T &&t): m1{t.m1}, m2{t.m2} {
if (current_cnt == MAX_CNT) {
throw std::runtime_error("T: maximum object count exceeded");
}
++current_cnt;
std::cout << "T move constructor called.\n";
}
T::~T() {
--current_cnt;
std::cout << "T destructor called.\n";
}
void T::adjust(int ratio) {
m1 *= ratio;
m2 *= ratio;
}
int T::get_cnt() {
return current_cnt;
}
void output(const T &t) {
std::cout << "(" << t.m1 << ", " << t.m2 << ")";
}
- task1.cpp
#include<iostream>
#include<utility>
#include"t.h"
void test() {
using std::cout;
using std::endl;
cout << "T info: " << T::doc << endl;
cout << "T objects'max count: " << T::MAX_CNT << endl;
cout << "T objects'current count: " << T::get_cnt() << endl << endl;
{
T t1;
cout << "t1 = ";
output(t1);
cout << endl;
T t2(3, 4);
cout << "t2 = ";
output(t2);
cout << endl;
T t3(t2);
t3.adjust(2);
cout << "t3 = ";
output(t3);
cout << endl;
T t4(std::move(t2));
cout << "t4 = ";
output(t4);
cout << endl;
cout << "test: T objects'current count: " << T::get_cnt() << endl;
}
cout << "test: T objects'current count: " << T::get_cnt() << endl;
}
int main() {
std::cout << "test Class T: \n";
test();
}
运行结果
问题回答
-
问题1
普通构造函数是是对变量直接赋值，在t2中，输入（3，4），则t2的两个int值则为3和4，如果没有输入任何数值则默认T中的2个变量为0，例如t1，未写任何值两个变量默认为0，复制构造函数是将其他同类的变量复制一遍在赋予到当前的变量中，例如t3，就是将t2的进行了复制，移动构造函数是将同类的变量直接移动到新变量中而不是复制，t4则是将t2的值直接移动到了t4中，析构函数的作用是在生命周期结束的变量进行清除，避免内存占用。 -
问题2
不能
![image]()
报错显示了重复定义，这违反了C++的单一定义原则，因为变量是在头文件中所定义，且被t.cpp与task1.cpp同时定义了一次，所以编译错误。 -
问题3
这4个变量属于局部作用域，生命周期为自动存储期。在t1期间，不能访问t1，t2的变量，因为他们属于private，不可访问，这体现了类的封装与访问控制。 -
问题4
![image]()
会被正常销毁，在出现异常时，析构函数依然会调用，在异常结果报告出来前将其正常销毁，避免内存的占用。
实验任务2
源代码
- Complex.h
#pragma once
#include<string>
class Complex{
public:
Complex(double r=0.0,double i=0.0);
Complex(const Complex &com);
~Complex();
static const std::string doc;
double real() const;
double imag() const;
void add(const Complex &com);
friend void output(const Complex &com);
friend double abs(const Complex &com);
friend Complex add(const Complex &com1,const Complex &com2);
friend bool is_equal(const Complex &com1,const Complex &com2);
friend bool is_not_equal(const Complex &com1,const Complex &com2);
private:
double re;
double im;
};
- Complex.cpp
#include<iostream>
#include<string>
#include<cmath>
#include<iomanip>
#include "Complex.h"
const std::string Complex::doc{"a simplified complex class"};
Complex::Complex(double r,double i):re{r},im{i}{}
Complex::Complex(const Complex &com):re{com.re},im{com.im}{}
Complex::~Complex(){}
double Complex::real() const{
return re;
}
double Complex::imag() const{
return im;
}
void Complex::add(const Complex &com){
re+=com.re;
im+=com.im;
}
void output(const Complex &com){
using namespace std;
if(com.im>=0) cout<<com.re<<" + "<<com.im<<"i"<<endl;
else cout<<com.re<<" - "<<-com.im<<"i"<<endl;
}
double abs(const Complex &com){
using namespace std;
double ab=sqrt(com.re*com.re+com.im*com.im);
return ab;
}
Complex add(const Complex &com1,const Complex &com2){
Complex com3;
com3.re=com1.re+com2.re;
com3.im=com1.im+com2.im;
return com3;
}
bool is_equal(const Complex &com1,const Complex &com2){
if(com1.re==com2.re&&com1.im==com2.im) return true;
else return false;
}
bool is_not_equal(const Complex &com1,const Complex &com2){
if(com1.re==com2.re&&com1.im==com2.im) return false;
else return true;
}
- task2.cpp
#include <iomanip>
#include <iostream>
#include <complex>
#include "Complex.h"
// 测试自定义类Complex
void test_Complex() {
using std::cout;
using std::endl;
using std::boolalpha;
cout << "类成员测试: " << endl;
cout << Complex::doc << endl << endl;
cout << "Complex对象测试: " << endl;
Complex c1;
Complex c2(3, -4);
Complex c3(c2);
Complex c4 = c2;
const Complex c5(3.5);
const Complex c6 = 3.5;
cout << "c1 = "; output(c1); cout << endl;
cout << "c2 = "; output(c2); cout << endl;
cout << "c3 = "; output(c3); cout << endl;
cout << "c4 = "; output(c4); cout << endl;
cout << "c5 = "; output(c5); cout << endl;
cout << "c6.real = " << c6.real()
<< ", c6.imag = " << c6.imag() << endl << endl;
cout << "复数运算测试: " << endl;
cout << "abs(c2) = " << abs(c2) << endl;
c1.add(c2);
cout << "c1 += c2, c1 = "; output(c1); cout << endl;
cout << boolalpha;
cout << "c1 == c2 : " << is_equal(c1, c2) << endl;
cout << "c1 != c2 : " << is_not_equal(c1, c2) << endl;
c4 = add(c2, c3);
cout << "c4 = c2 + c3, c4 = "; output(c4); cout << endl;
}
// 测试标准库类模板complex
void test_std_complex() {
using std::cout;
using std::endl;
using std::boolalpha;
cout << "std::complex<double>对象测试: " << endl;
std::complex<double> c1;
std::complex<double> c2(3, -4);
std::complex<double> c3(c2);
std::complex<double> c4 = c2;
std::complex<double> c5 = 3.5;
const std::complex<double> c6(3.5);
cout << "c1 = " << c1 << endl;
cout << "c2 = " << c2 << endl;
cout << "c3 = " << c3 << endl;
cout << "c4 = " << c4 << endl;
cout << "c5 = " << c5 << endl;
cout << "c6.real = " << c6.real()
<< ", c6.imag = " << c6.imag() << endl << endl;
cout << "复数运算测试: " << endl;
cout << "abs(c2) = " << abs(c2) << endl;
c1 += c2;
cout << "c1 += c2, c1 = " << c1 << endl;
cout << boolalpha;
cout << "c1 == c2 : " << (c1 == c2)<< endl;
cout << "c1 != c2 : " << (c1 != c2) << endl;
c4 = c2 + c3;
cout << "c4 = c2 + c3, c4 = " << c4 << endl;
}
int main() {
std::cout << "*******测试1: 自定义类Complex*******\n";
test_Complex();
std::cout << "\n*******测试2: 标准库类模板complex*******\n";
test_std_complex();
}
运行截图
问题回答
-
问题1
1.1 在返回real和imag的函数中，后面需要加上const。如果不加，则有报错：
![image]()
图像中的则表示一个const常量去调用一个非const成员函数，有修改值的可能性，从而导致编译错误。
1.2不能通过，因为c6是const，如果add则会触发常量被修改的风险，这体现了类的数据保护机制。 -
问题2
标准库的用法更加简洁，其中的运算符与函数名称定义基本相同。 -
问题3
必须的，因为类中的两个变量是私有的，如果不加friend的话是无法直接访问到类中的2个变量的，所以必须加上friend，以共享自己的private变量，方便运算。
实验任务3
源代码
- PlayerControl.h
#pragma once
#include <string>
enum class ControlType {Play, Pause, Next, Prev, Stop, Unknown};
class PlayerControl {
public:
PlayerControl();
ControlType parse(const std::string& control_str); // 实现std::string --> ControlType转换
void execute(ControlType cmd) const; // 执行控制操作（以打印输出模拟）
static int get_cnt();
private:
static int total_cnt;
};
- PlayerControl.cpp
#include "PlayerControl.h"
#include <algorithm>
#include <iostream>
int PlayerControl::total_cnt = 0;
PlayerControl::PlayerControl() {}
// 待补足
// 1. 将输入字符串统一成转为小写，实现大小写不敏感
// 2. 匹配"play"/"pause"/"next"/"prev"/"stop"并返回对应枚举；
// 未匹配的字符串返回ControlType::Unknown
ControlType PlayerControl::parse(const std::string& control_str) {
std::string s,s1;
s1=control_str;
int len=s1.length();
for(int i=0;i<len;i++) s+=tolower(s1[i]);
if(s=="play") return ControlType::Play;
else if(s=="pause") return ControlType::Pause;
else if(s=="next") return ControlType::Next;
else if(s=="prev") return ControlType::Prev;
else if(s=="stop") return ControlType::Stop;
else return ControlType::Unknown;
}
void PlayerControl::execute(ControlType cmd) const {
// 每执行一次控制操作（含未知命令），total_cnt自增 1
++total_cnt;
switch (cmd) {
case ControlType::Play: std::cout << "[play] Playing music...\n"; break;
case ControlType::Pause: std::cout << "[Pause] Music paused\n"; break;
case ControlType::Next: std::cout << "[Next] Skipping to next track\n"; break;
case ControlType::Prev: std::cout << "[Prev] Back to previous track\n"; break;
case ControlType::Stop: std::cout << "[Stop] Music stopped\n"; break;
default: std::cout << "[Error] unknown control\n"; break;
}
}
int PlayerControl::get_cnt() {
return total_cnt;
}
+task3.cpp
#include "PlayerControl.h"
#include <algorithm>
#include <iostream>
int PlayerControl::total_cnt = 0;
PlayerControl::PlayerControl() {}
// 待补足
// 1. 将输入字符串统一成转为小写，实现大小写不敏感
// 2. 匹配"play"/"pause"/"next"/"prev"/"stop"并返回对应枚举；
// 未匹配的字符串返回ControlType::Unknown
ControlType PlayerControl::parse(const std::string& control_str) {
std::string s,s1;
s1=control_str;
int len=s1.length();
for(int i=0;i<len;i++) s+=tolower(s1[i]);
if(s=="play") return ControlType::Play;
else if(s=="pause") return ControlType::Pause;
else if(s=="next") return ControlType::Next;
else if(s=="prev") return ControlType::Prev;
else if(s=="stop") return ControlType::Stop;
else return ControlType::Unknown;
}
void PlayerControl::execute(ControlType cmd) const {
// 每执行一次控制操作（含未知命令），total_cnt自增 1
++total_cnt;
switch (cmd) {
case ControlType::Play: std::cout << "[play] Playing music...\n"; break;
case ControlType::Pause: std::cout << "[Pause] Music paused\n"; break;
case ControlType::Next: std::cout << "[Next] Skipping to next track\n"; break;
case ControlType::Prev: std::cout << "[Prev] Back to previous track\n"; break;
case ControlType::Stop: std::cout << "[Stop] Music stopped\n"; break;
default: std::cout << "[Error] unknown control\n"; break;
}
}
int PlayerControl::get_cnt() {
return total_cnt;
}
运行截图
问题回答
由于const保护的是对象自身的非静态成员函数，而static数据是独立于对象而存在的，在任何地方或者函数中都可以被操作修改。
实验任务4
源代码
- Fraction.h
#pragma once
#include<string>
class Fraction{
public:
Fraction(int up0=1,int down0=1);
Fraction(const Fraction &fra);
~Fraction();
static const std::string doc;
int get_up() const;
int get_down() const;
Fraction negative();
friend void output(const Fraction &fra);
friend Fraction add(const Fraction &fra1,const Fraction &fra2);
friend Fraction sub(const Fraction &fra1,const Fraction &fra2);
friend Fraction mul(const Fraction &fra1,const Fraction &fra2);
friend Fraction div(const Fraction &fra1,const Fraction &fra2);
private:
int up;
int down;
};
- Fraction.cpp
#include <iostream>
#include <stdexcept>
#include "Fraction.h"
const std::string Fraction::doc{"Fraction类 v 0.01版.目前仅支持分数对象的构造、输出、加/减/乘/除运算"};
int gcd(int a,int b){
a=std::abs(a);
b=std::abs(b);
while(b!=0){
int tmp=b;
b=a%b;
a=tmp;
}
return a;
}
Fraction::Fraction(int up0,int down0):up{up0},down{down0}{
if(down==0)
throw std::invalid_argument("Fraction: 分母不能为0");
if(up*down<0){
down=std::abs(down);
up=up<0?up:-up;
}
}
Fraction::Fraction(const Fraction &fra):up{fra.up},down{fra.down}{}
Fraction::~Fraction(){}
int Fraction::get_up() const{
return up/gcd(up,down);
}
int Fraction::get_down() const{
return down/gcd(up,down);
}
Fraction Fraction::negative(){
Fraction fra;
fra.up=-up;
fra.down=down;
return fra;
}
void output(const Fraction &fra){
int up=fra.up,down=fra.down;
int yueshu=gcd(up,down);
up/=yueshu;
down/=yueshu;
if(up*down>=0){
up=std::abs(up);
down=std::abs(down);
}
if(down==0) throw std::invalid_argument("Fraction: 分母不能为0");
else if(down!=1) std::cout<<up<<"/"<<down<<std::endl;
else std::cout<<up<<std::endl;
}
Fraction add(const Fraction &fra1,const Fraction &fra2){
Fraction fra;
int up1=fra1.up,down1=fra1.down;
int up2=fra2.up,down2=fra2.down;
int down=down1*down2;
int up=up1*down2+up2*down1;
fra.up=up;
fra.down=down;
return fra;
}
Fraction sub(const Fraction &fra1,const Fraction &fra2){
Fraction fra;
int up1=fra1.up,down1=fra1.down;
int up2=fra2.up,down2=fra2.down;
int down=down1*down2;
int up=up1*down2-up2*down1;
fra.up=up;
fra.down=down;
return fra;
}
Fraction mul(const Fraction &fra1,const Fraction &fra2){
Fraction fra;
int up1=fra1.up,down1=fra1.down;
int up2=fra2.up,down2=fra2.down;
int down=down1*down2;
int up=up1*up2;
fra.up=up;
fra.down=down;
return fra;
}
Fraction div(const Fraction &fra1,const Fraction &fra2){
Fraction fra;
int up1=fra1.up,down1=fra1.down;
int up2=fra2.down,down2=fra2.up;
if(up2*down2<0){
down2=std::abs(down2);
up2=up2<0?up2:-up2;
}
int down=down1*down2;
int up=up1*up2;
fra.up=up;
fra.down=down;
return fra;
}
- task4.cpp
#include <iostream>
#include "Fraction.h"
void test1() {
using std::cout;
using std::endl;
cout << "Fraction类测试: " << endl;
cout << Fraction::doc << endl << endl;
Fraction f1(5);
Fraction f2(3, -4), f3(-18, 12);
Fraction f4(f3);
cout << "f1 = "; output(f1); cout << endl;
cout << "f2 = "; output(f2); cout << endl;
cout << "f3 = "; output(f3); cout << endl;
cout << "f4 = "; output(f4); cout << endl;
const Fraction f5(f4.negative());
cout << "f5 = "; output(f5); cout << endl;
cout << "f5.get_up() = " << f5.get_up()
<< ", f5.get_down() = " << f5.get_down() << endl;
cout << "f1 + f2 = "; output(add(f1, f2)); cout << endl;
cout << "f1 - f2 = "; output(sub(f1, f2)); cout << endl;
cout << "f1 * f2 = "; output(mul(f1, f2)); cout << endl;
cout << "f1 / f2 = "; output(div(f1, f2)); cout << endl;
cout << "f4 + f5 = "; output(add(f4, f5)); cout << endl;
}
void test2() {
using std::cout;
using std::endl;
Fraction f6(42, 55), f7(0, 3);
cout << "f6 = "; output(f6); cout << endl;
cout << "f7 = "; output(f7); cout << endl;
cout << "f6 / f7 = "; output(div(f6, f7)); cout << endl;
}
int main() {
std::cout << "测试1: Fraction类基础功能测试\n";
test1();
std::cout << "\n测试2: 分母为0测试: \n";
test2();
}
运行截图
问题回答
我选择的是分数类加友元函数。因为要操作的函数很多，所以需要进行分离，让Fraction这个类只负责数据的承接载体，有友元函数来完成加减乘除的操作，这样做可以将运算和输出分离出类，让类内部更加简洁。
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